Dynamic mass spectrometer

Abstract

A pulse-type ion source derived from a pulse laser produced plasma provides an ion beam which is analyzed in a time-dependent field which varies monotonically as an inverse function of time for the pulse period. Ions of common charge to mass ratio are collected at different points after executing a trajectory, which, because of the time dependent nature of the field, traverses the same path for ions of the same charge to mass ratio, irrespective of their initial velocity when entering the field; thus, facilitating the determination of the mass, charge and energy spectrums of the entire population of particles emitted in pulses or bursts, simultaneously and even from individual bursts.

What is claimed is: 
     
       1. The method of mass spectrometry which comprises the steps of projecting a beam of particles which can have a wide range of kinetic energy into an analyzing region, establishing a field in said region in a direction transverse to the direction of said beam which field deflects said particles independently of their initial kinetic energy as they enter said region along paths of length which are dependent upon the mass and charge of said particles, and collecting said deflected particles at points spaced along said region from the place of entry of said beam into said region. 
     
     
       2. The invention as set forth in claim 1 wherein said field is established by varying said field over a period of time as an inverse function of time. 
     
     
       3. The invention as set forth in claim 1 including the step of projecting said beam in pulses, and initiating said field variation upon the onset of each of said pulses. 
     
     
       4. The invention as set forth in claim 2 wherein said field is an electric field, and said step of varying produces a variation of the intensity, E, of said field in said region of the form E =E o  /(T+t) 2  where Eo is the maximum intensity of said field and (T+t) is the elapsed time from the onset of each of said pulses. 
     
     
       5. The invention as set forth in claim 3 wherein said field is a magnetic field, and said step of varying produces a variation in the flux density, B, of said field in said region of the form B = B o  /T+t) where Bo is the maximum flux density of said field and (T+t) is the elapsed time from the onset of each of said pulses. 
     
     
       6. The invention as set forth in claim 3 wherein said beam is produced by the step of projecting a pulse of radiant energy upon a sample to produce a plasma. 
     
     
       7. The invention as set forth in claim 1 including the step of detecting said radiant energy pulse, and initiating the onset of said field variation upon the detection of said radiant energy pulse. 
     
     
       8. The invention set forth in claim 6 including the step of forming said radiant energy pulse with a pulse laser. 
     
     
       9. The invention as set forth in claim 1 including the step of collecting said particles at a plurality of points spaced at different distances from the entrance of said beam into said region. 
     
     
       10. The invention as set forth in claim 9 including the step of processing the currents due to the particles collected at said points to determine the elemental composition of the material which produces said beam. 
     
     
       11. The invention as set forth in claim 10 wherein said processing step includes the step of measuring the variation of said currents at said collection points for a period of time to determine the energy of elemental constituents of the material which produces said beam. 
     
     
       12. A mass spectrometer adapted to analyze charged particles having a wide range of kinetic energy which comprises means defining a region for deflection of said charged particles to collection points spaced along said region from the place of entry of said particles into said region, means for establishing a field in said region which provides trajectories to said collection points independent of the initial kinetic energy of said particles upon entry into said region and dependent upon their charge to mass (q/m) ratio, said field being in a direction transverse to the direction of travel of said particles along said trajectories, and means for collecting said particles at said collection points.   
     
     
       13. The invention as set forth in claim 12 wherein said field establishing means includes means for producing a field which varies as an inverse function of time for a predetermined period of time. 
     
     
       14. The invention as set forth in claim 13 wherein said field producing means includes means responsive to the presence of said particles for initiating the variation of said field. 
     
     
       15. The invention as set forth in claim 14 wherein said field producing means includes means operated by said initiating means for continuing the variation of said field for a period of time commensurate with the period of time said particles are present. 
     
     
       16. The invention as set forth in claim 13 wherein said field establishing means includes means for providing an electric field in said region having an intensity, E, of the form E= e o  /(t+t) 2   where Eo is the maximum intensity of said field and (T+t) is elapsed time.     
     
     
       17. The invention as set forth in claim 13 wherein said field establishing means includes means for providing an electric field in said region having a flux density B of the form B = b o  /(T+t) where Bo is the maximum flux density and T+ t is time.     
     
     
       18. The invention as set forth in claim 13 including means for defining a path for a beam of ions which constitute said particles into an entrance into said region, and said collecting means includes a plurality of ion collectors each spaced at a different distance along a path extending from said entrance. 
     
     
       19. The invention as set forth in claim 18 includes means for providing said beam in bursts. 
     
     
       20. The invention as set forth in claim 19 wherein said burst providing means comprises a pulse laser which directs a laser beam upon a sample for ionizing material in said sample to produce a plasma which provides said beam. 
     
     
       21. The invention as set forth in claim 20 including means responsive to the presence of said laser beam for providing an output on the onset thereof, and means responsive to said output for operating said field establishing means for producing said field for a predetermined period of time commensurate with the lifetime of said plasma produced by the laser pulse. 
     
     
       22. The invention as set forth in claim 23 including means connected to each of said collectors for processing signals corresponding to the current due to the ions collected thereat for determining the elemental composition of said plasma. 
     
     
       23. The invention as set forth in claim 21 including means connected to said collectors for measuring the current due to the ions collected therein as a function of time for determining the energy distribution of the elements of which said plasma is constituted. 
     
     
       24. The invention as set forth in claim 16 wherein said field estblishing means includes a pair of conductive plates spaced from each other, one of said plates having an entrance aperture for said particle beam and a plurality of exit apertures spaced from said entrance aperture each at a different distance along a linear path extending from said entrance aperture, and said collecting means includes a plurality of conductive members each adjacent a different one of said exit apertures on the side thereof said one plate opposite the side thereof which faces said other plate. 
     
     
       25. The invention as set forth in claim 24 including a plurality of rings disposed between said plates and electrically connected thereto for providing uniformity of the field in the periphery of said region. 
     
     
       26. The invention as set forth in claim 24 wherein said field establishing means includes digital to analog converter means, means for providing a train of repetitive pulses of certain repetition rate, means for counting said pulses to provide a digital input to said converter, means for inhibiting said counting means when a certain number of pulses which occur during said predetermined period of time are counted, and means operated by said converter for providing a high voltage for producing a voltage of said form and means for applying said voltage across said plates.